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104. Maximum Depth of Binary Tree ​

题目 ​

Given the root of a binary tree, return its maximum depth.

A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

 

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: 3

Example 2:

Input: root = [1,null,2]
Output: 2

 

Constraints:

  • The number of nodes in the tree is in the range [0, 104].
  • -100 <= Node.val <= 100
Related Topics
  • 树
  • 深度优先搜索
  • 广度优先搜索
  • 二叉树

  • 👍 1992
  • 👎 0

    • 解法 ​

    py
    # leetcode submit region begin(Prohibit modification and deletion)
# Definition for a binary tree node.
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:

        def dfs(root, height) -> int:
            if not root:
                return height

            return max(dfs(root.left, height + 1),  dfs(root.right, height + 1))

        return dfs(root, 0)




# leetcode submit region end(Prohibit modification and deletion)

    复杂度分析 ​

    • N 为二叉树的节点, H 为二叉树的高度
    • 时间复杂度 O(N)
    • 空间复杂度 O(H)